Motor vehicle manufacturers aim to eliminate rattles and other undesired noises which might occur when a vehicle is in use. However since these noises only occur when the vehicle is subjected to the vibrations occurring in use, it can be difficult to track down and correct the source of such noises.
A number of different simulation systems have been developed to allow identification of noises on a test bed. Roller tests are known in which the stationary car has its wheel driven on sets of rollers, which have different surface texture at the left, center and right hand portions of the rollers. The car can also be subjected to different frequencies of vibration by changing the rotational speed of the rollers. This system has the disadvantage that it is dangerous to approach or leave the car, since its wheels are running on rollers, and it may move suddenly from side to side.
A state of the art system is the Hydropulse.TM. computer-controlled road simulator in which each wheel may be independently vibrated while resting on a support pillar. Each pillar can move in unison, or the pillars may be driven according to actual recorded road data. It can be very difficult to determine by ear the source of a noise, even with such controlled vibration systems, owing to the complex acoustics within the car body parts. It is known to use microphones, which may be fixed or moved around inside the test vehicle, and measure sound intensity or perform Fourier frequency analysis. It is also known to use triangulation by microphone. However, these techniques are expensive and time consuming to set up on the test vehicle, and rely heavily on operator expertise.